The present invention relates to a method of and an apparatus for making preforms from a pourable but at most limitedly flowable substance for subsequent use in producing three-dimensional profiled articles, particularly for use in connection with a substance which is a mixture of fillers and binders.
There have already been proposed many methods of and apparatuses for producing three-dimensionally profiled articles, such as table tops, windows, pallets and similar objects, among them such in which a mixture of chip-shaped or filamentary materials with a binder, such as a mixture of comminuted, cellulose-containing particles with a binder which hardens at an elevated temperature, that is, a thermosetting synthetic plastic material, is filled into a lower mold part of a compression mold in such a manner that the substance or mixture assumes a shape on the lower mold part which corresponds, in a certain proportion, either to the final shape of the article to be produced, or to the density to be achieved throughout or in selected regions of the article. Usually, the thickness of the layer of the mixture in the compression mold amounts to 4 to 7 times the thickness of the finished profiled article at the particular region thereof. When the compression mold is a pre-compression mold, then the mixture filled into the lower mold part of the mold is pre-compressed in the latter by a compressing mold or tool, and the mixture is compacted to almost its final density. The strength of the thus made preform is sufficient for preventing deformation or disintegration thereof during the withdrawal thereof from the pre-compressing mold or tool arrangement. After that, the preform is inserted into a hot compressing mold, possibly after or simultaneously with coating with a protective or decorative layer, and the preform obtains its final shape in the hot compressing mold, under the influence of pressure and elevated temperature, and the thus-obtained article hardens and, possibly, is simultaneously provided with a decorative or protective layer. On the other hand, the above-mentioned mold which is being filled with the mixture may be a hot compressing mold in which the article is directly produced without the intermediary of the preform.
The quality of the pressed profiled article depends on the fact whether or not it possesses, throughout, the density and/or fibrous structure which are necessary for the achievement of the desired mechanical properties. These properties are, to a great extent, dependent on the fact what degree of care has been exercised during the filling of the mixture into the lower mold. Heretofore, the filling has been accomplished, during the production of profiled articles of non-excessive dimensions, in such a manner that a predetermined and metered amount of the mixture has been admitted to the lower mold either out of a measuring container or, by means of an automatic metering arrangement, from a storage container, after which such a predetermined metered amount has been manually distributed over the lower mold either uniformly, or non-uniformly, dependent on the particular requirements. It will be appreciated that, when the metered amount of the mixture is distributed in this manner, the desired properties throughout the article are very rarely, if ever, achieved and, many a time, such properties are left, to a large degree, to chance.